Tanglewood 2006 may well be remembered as the summer of James Levine’s Don Giovanni. The opera that’s often referred to as Mozart’s greatest, or at least his most ambitious, like King Lear almost never completely succeeds in performance. There’s just too much in it — comedy and tragedy (it’s called a dramma giocoso — a jocular drama) and large, even cosmic, issues of morality, personal liberty, the pleasures of sexual excess (as a means of self-definition) and the torments of Hell. Lorenzo da Ponte’s libretto is brilliantly constructed, and Mozart’s music is one of the glories of Western culture. But last weekend, Levine assembled a remarkable cast of singers who could also act, and he led the BSO, at the top of its game, in a magnificent realization of this astonishing masterwork. This “semi-staged” concert version captured more completely than any fully staged performance I’ve ever seen, and with quicksilver fluidity, both the opera’s high hilarity and its dark profundity.

As Don Giovanni, charismatic young Polish baritone Mariusz Kwiecien (kvee-AY-chen) did nothing to diminish this ruthless aristocrat’s despicability, his relentless search for self-gratification at anyone’s expense. Yet with his powerful, Burgundy-rich voice and startling good looks, how could anyone not be seduced? And how could one not admire him for living completely on his own terms, even to resist eternal damnation, going to Hell for his refusal to accept the conventional morality of his inferiors? He tossed off the tongue-twisting patter of the “Champagne Aria” with glittering abandon and the mandolin serenade with languorous allure.

Two late substitutions were also welcome ones. Georgian soprano Tamar Iveri replaced Barbara Frittoli as the raped Donna Anna and sang with heroic power, luscious warmth, and impassioned dignity. As Leporello, Giovanni’s reluctant manservant, young Italian bass-baritone Luca Pisaroni (replacing veteran Ferruccio Furlanetto), pointed every phrase with comic mastery, and he brought the house down with the aria cataloguing his master’s conquests. (The catalogue itself was the opera’s thick score, handed to Leporello by Levine himself.) Changing places with Giovanni, this Leporello also did a devilishly accurate imitation of his master’s voice.

I was struck by the way each of Giovanni’s three attempted victims — Anna, the seduced and abandoned Donna Elvira (who still loves him), and the peasant girl Zerlina (on her wedding day!) — sang in a different timbre. Finnish soprano Soile Isokoski, with a lighter voice than Iveri, made a comic but deeply touching Elvira. (She perused that catalogue with horrified disbelief.) American soprano Heidi Grant Murphy, a favorite of Levine’s, was almost too lightweight for Zerlina, but she had flair and a silvery tone.

The singer with the hardest job was also one of the most successful. Don Ottavio, Anna’s fiancé, can be a pretty thankless role. Despite singing two of Mozart’s most ravishing tenor arias, he still comes off as blandly ineffectual. But American tenor Matthew Polenzani has perhaps the finest tenor voice of his generation, and he sang with aristocratic elegance and potency. Although his situation was hopeless, he was a man in control. When Anna admits that for a moment she thought he was the man who had invaded her room, you could believe it was possible. I’ve never heard Ottavio’s first aria, “Dalla sua pace” (“On her peace mine depends”), sung more beautifully or expressively. Baritone Patrick Carfizzi was a pathetically sweet Masetto, Zerlina’s hapless fiancé, and bass Morris Robinson, who only a few years ago graduated from BU’s Opera Institute, then with the Boston Lyric Opera sang the Commendatore, Anna’s murdered father, and, later, his ghostly statue, repeated that role with even greater success in more stellar company.